A. Technical Field
The present invention relates to: a paint composition for in-mold coating, which is suitable for in-mold coating to thermoplastic plastic substrates such as polyolefins; and a thermoplastic plastic molding which involves the use of this paint composition.
B. Background Art
Polyolefinic resins, which are typical as thermoplastic plastics, have various excellent properties such as moldability, chemical resistance, heat resistance, water resistance, and good electrical properties and are inexpensive, so they have hitherto widely been utilized as plastic moldings for such as home electric appliances and automobile parts. In addition, as the case may be, these plastic moldings are decorated by in-mold coating.
However, prior paint compositions for in-mold coating have had problems in that: if thermosetting resins or polar materials are used as substrates, then the prior paint compositions may be able to exercise sufficient adhesion, but, if nonpolar materials such as the polyolefinic resins are used as substrates, then the adhesion is so insufficient as to result in failure to obtain sufficient paint film performances. Furthermore, paint compositions used for in-mold coating are required to have not only the adhesion to substrates but also the flowability for injecting the composition into a narrow cavity in a mold. However, as to the prior paint compositions for in-mold coating, this flowability has also been insufficient.
Thus, as solution of these problems, there is proposed a paint composition for in-mold coating of thermoplastic plastic substrates, which comprises: an acryl-modified polyolefin; a reactive oligomer and/or a reactive monomer; and a radical polymerization initiator; in a specific ratio (refer to patent document 1 below).
[Patent Document 1] JP-A-249680/2002 (Kokai)
However, the paint composition for in-mold coating which is described in the aforementioned patent document 1 has had a problem in that: it may have satisfactory performances in points of the adhesion to nonpolar materials and the flowability, but, if the temperature of the mold during the molding operation is higher than the melting point of the above composition, then, in order to prevent the paint film from peeling off during the mold-releasing operation, the mold must be cooled and then opened. As a means of solving this problem, it can be conceived to raise the melting point of the composition. However, as to the paint composition for in-mold coating which is described in the aforementioned patent document 1, another problem that the resultant paint film becomes turbid has been found to occur, from the present inventor's attempt to use an acryl-modified polyolefin of a high melting point in order to raise the melting point of the composition.